About 3 to 5 million years ago, the valley
that would become the Tahoe Basin sank
between parallel fractures in the Earth’s
crust as the mountains on either side
continued to rise. A shallow lake began to
form in the resulting valley.
Roughly 2 to 3 million years ago, erupting
volcanoes blocked the outlet, forcing the
lake to rise hundreds of feet above its
current elevation, and eventually eroded
down to near its current outlet.
Between 1 million and 20,000 years ago,
large masses of glacial ice covered the west
side of the Tahoe Basin. Current geologic
theory suggests an earthen berm (moraine)
left by a receding glacier near Olympic
Valley acted as a dam, causing the lake level
to rise and then draw down rapidly when
the dam catastrophically failed. Between

7,000 and 15,000 years ago, a four-mile
segment of the West Shore collapsed into
the Lake causing a massive submerged
debris avalanche, widening the Lake by
three miles and creating McKinney Bay.1
The Tahoe Basin is mostly granite, with
little topsoil, and therefore few nutrients
have washed into the lake to promote the
growth of algae and other organisms that
make water murky.
As well, 40 percent of the precipitation
falling into the Tahoe Basin lands directly
on the lake. The remaining precipitation
drains through the decomposed granite soil
found in marshes and meadows, creating a
good filtering system for water.
Urbanization of the Tahoe Basin has
eliminated 75 percent of its marshes, 50
percent of its meadows and 35 percent of its
steam zone habitats. About 85 percent of all
wildlife in the Tahoe Basin use these habitats.

About the lake
Lake Tahoe is located in the states of
California and Nevada, with two-thirds in
California. It is fed by 63 streams and two
hot springs.
The Truckee River is Tahoe’s only outlet
and flows from the dam in Tahoe City east
through Reno and eventually drains into
Pyramid Lake in the Nevada desert.
However, water releases are not permitted
when the lake surface level falls below
the natural rim at 6,223.’ The lowest lake
level on record (measured since 1900) was
6,220.26’ on Nov. 30, 1992.
The Lake of the Sky appears blue in color
as other colors in the light spectrum are
absorbed and blue light is scattered back.

Lake clarity
The University of California, Davis,
operates the Tahoe Environmental Resarch
Center, which monitors, among other

things, the clarity of Lake Tahoe. Clarity
has been measured since 1968 and was first
recorded at 102.4’.
The waters of Lake Tahoe were clear
to an average depth of 73.1’ in 2015. The
lowest average depth on record was 64.1’
in 1997. Lake Tahoe is losing clarity because of algae growth fueled by nitrogen
and phosphorus.

Lake Tahoe’s discovery
The first recorded discovery of Lake Tahoe
by white explorers was on Feb. 14, 1844,
when John Charles Frémont and Charles
Preuss spotted the lake from atop Red Lake
Peak. The lake went through several names
before it was officially named Tahoe in 1945.
Tahoe is a mispronunciation of the
first two syllables of the Washoe’s word for
the lake – Da ow a ga, which means “edge
of the lake.” 

Learn more: Visit the Tahoe Science Center in Incline Village or tahoesciencecenter.org. Sources: Tahoe Environmental Research Center, U.S. Geological Survey, U.S. Forest Service, “Tahoe Place Names” and David Antonucci (denoted by 1).